From: Mike Kravetz <mike.kravetz@oracle.com>
To: Peter Xu <peterx@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Axel Rasmussen <axelrasmussen@google.com>,
Matthew Wilcox <willy@infradead.org>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 2/4] hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled
Date: Wed, 17 Feb 2021 17:34:03 -0800 [thread overview]
Message-ID: <bf4c509b-18d0-a575-81c2-b089f7b2f05c@oracle.com> (raw)
In-Reply-To: <20210217204619.54761-1-peterx@redhat.com>
On 2/17/21 12:46 PM, Peter Xu wrote:
> Huge pmd sharing could bring problem to userfaultfd. The thing is that
> userfaultfd is running its logic based on the special bits on page table
> entries, however the huge pmd sharing could potentially share page table
> entries for different address ranges. That could cause issues on either:
>
> - When sharing huge pmd page tables for an uffd write protected range, the
> newly mapped huge pmd range will also be write protected unexpectedly, or,
>
> - When we try to write protect a range of huge pmd shared range, we'll first
> do huge_pmd_unshare() in hugetlb_change_protection(), however that also
> means the UFFDIO_WRITEPROTECT could be silently skipped for the shared
> region, which could lead to data loss.
>
> Since at it, a few other things are done altogether:
>
> - Move want_pmd_share() from mm/hugetlb.c into linux/hugetlb.h, because
> that's definitely something that arch code would like to use too
>
> - ARM64 currently directly check against CONFIG_ARCH_WANT_HUGE_PMD_SHARE when
> trying to share huge pmd. Switch to the want_pmd_share() helper.
>
> Since at it, move vma_shareable() from huge_pmd_share() into want_pmd_share().
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> arch/arm64/mm/hugetlbpage.c | 3 +--
> include/linux/hugetlb.h | 2 ++
> include/linux/userfaultfd_k.h | 9 +++++++++
> mm/hugetlb.c | 20 ++++++++++++++------
> 4 files changed, 26 insertions(+), 8 deletions(-)
Thanks,
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
--
Mike Kravetz
next prev parent reply other threads:[~2021-02-18 1:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-17 20:44 [PATCH v2 0/4] hugetlb: Disable huge pmd unshare for uffd-wp Peter Xu
2021-02-17 20:44 ` [PATCH v2 1/4] hugetlb: Pass vma into huge_pte_alloc() and huge_pmd_share() Peter Xu
2021-02-17 20:46 ` [PATCH v2 2/4] hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled Peter Xu
2021-02-17 20:46 ` [PATCH v2 3/4] mm/hugetlb: Move flush_hugetlb_tlb_range() into hugetlb.h Peter Xu
2021-02-17 20:46 ` [PATCH v2 4/4] hugetlb/userfaultfd: Unshare all pmds for hugetlbfs when register wp Peter Xu
2021-02-18 1:46 ` Mike Kravetz
2021-02-18 17:55 ` Peter Xu
2021-02-18 18:32 ` Axel Rasmussen
2021-02-18 20:32 ` Peter Xu
2021-02-18 20:34 ` Axel Rasmussen
2021-02-18 20:41 ` Peter Xu
2021-02-18 1:34 ` Mike Kravetz [this message]
2021-02-18 18:54 ` [PATCH v2 0/4] hugetlb: Disable huge pmd unshare for uffd-wp Axel Rasmussen
2021-02-18 20:33 ` Peter Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=bf4c509b-18d0-a575-81c2-b089f7b2f05c@oracle.com \
--to=mike.kravetz@oracle.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=axelrasmussen@google.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=peterx@redhat.com \
--cc=rppt@linux.vnet.ibm.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).